This invention refers to refrigeration or air conditioning systems which use capillary tubes as a control element and, more specifically, to a blocking valve for these systems.
Refrigeration and air conditioning systems essentially consist of a compressor, a condenser, a capillary tube and an evaporator.
In these systems, when the evaporator temperature reaches a predetermined value and the compressor is switched off, there occurs the migration of the heated fluid from the condenser side (the high pressure side) to the evaporator (low pressure side). This migration of the refrigerant to the evaporator at each stop of the compressor causes a loss of the cooling capacity in the system (approximately 6% in systems which use reciprocating compressors and 12% in systems which use rotary compressors), since the refrigerant, besides heating the evaporator, must be compressed once again at each new start of the compressor, when the normal operation cycle of the system is reestablished, that is, when the pressure and temperature levels are reestablished in each unit of the system.
A first known solution to solve this problem involves the use of a solenoid valve, installed between the condensor and the capillary tube. In this type of system, the valve is energized simultaneously with the stop of the compressor (rotary compressor), preventing the refrigerant from flowing from the condenser to the evaporator.
One problem of this solution is that the valve remains energized during the stop of the refrigeration system, and consequently, during the stop of the compressor, consuming during that time a considerable amount of energy.
Another known solution is described in the patent document GB 2121942 A. This system includes a one-way valve (26) installed between the suction side (21a) of a compressor (21) and the evaporator (25) to prevent the refrigerant flow from the side of the suction to the evaporator. A pressure responsive type valve (37) is installed between the condenser and the evaporator (25) to prevent the flow of the fluid from the condenser (22) to the evaporator (25) during the stop of the compressor (21). A connection tube (34) is connected between the valve (37) and the suction side (21a) of the compressor (21) to transmit the pressure from the suction side to the valve. The closure of the valve (37) is controlled by the suction pressure from the compressor (21). When the compressor (21) suction pressure becomes higher than a given predetermined value, it acts on the valve (37) preventing the passage of the refrigerant fluid from the condenser to the evaporator.
This solution has the inconvenience that it can only be applied to refrigeration systems which use rotary compressors, since this valve (37) is controlled by the pressure of the refrigerant gas which returns through the suction line during compressor (21) stops.
This return of the refrigerant gas through the suction line after the compressor stops, occurs due to the constructive characteristics of the rotary compressors. In this type of compressor, the refrigerant gas, discharged at a high pressure into the housing, leaks through the mechanical assembly to the suction side, which effect is used to activate the valve (37).
In reciprocating compressors, this effect of the refrigerant gas leakage through the mechanical assembly to the suction line does not occur, thus making impossible the use of this type of valve in systems using reciprocating compressors. Another inconvenience of this solution is the number of welds to be performed in the tubing due to the requirement of at least one additional tube (34) in the refrigeration circuit. This tube (34) is required for measuring the pressure of the suction line (21a).